The principal goal of this project is to develop a three- dimensional cardiac simulator: a computer model of the heart, its valves, and the nearby great vessels. The cardiac simulator will make possible a new mode of cardiac investigation, the computer experiment, in which the investigator has complete control over each individual experimental variable and complete access to all experimental data as output (without any interference between the simulated measurement and the simulated experiment). In order to test the cardiac simulator and simultaneously to elucidate certain aspects of diagnostic cardiac imaging, the project includes plans to simulate color-Doppler flow imaging, echocardiography, contrast angiography, nuclear medicine (gated blood-pool) imaging, and possibly magnetic resonance imaging. To the extent that the simulated images agree with the corresponding clinical images, this will provide support for the validity of the model. Given such agreement, moreover, one can use the known underlying situation in the simulated case to enhance the utility of the diagnostic technique. Applications of the proposed cardiac simulator are planned in three principal areas: (1) design of prosthetic cardiac valves, (2) computer models of diseases affecting mechanical function of the heart or its valves, and (3) studies on normal physiology and functional anatomy. In prosthetic valve design,, parametric studies are planned in which the cardiac simulator will be used to optimize valve performance with respect to pressure drop, net stroke volume, and thrombogenesis. Computer models of disease processes will include valve pathology such as stenosis and regurgitation, specific syndromes involving the valves such as Mitral Valve Prolapse Syndrome and idiopathic Hypertrophic Subaortic Stenosis, and conditions in which wall motion abnormal such as ventricular aneurism. In the area of functional anatomy and physiology, studies are planned to elucidate the normal function of the heart. Such studies will be based on systematic variation of cardiac parameters about their normal values to observe the effect on cardiac function. This work should reveal "design" principles which may be useful in the actual design of artificial hearts. Another planned study in the area of physiology is concerned with the acute and chronic adaptation of the heart to exercise. Aside from its intrinsic interest, this study will also make it possible for us to test prosthetic valves under exercise conditions. The work described above is all concerned with the adult heart. In addition, the project involves a series of studies related to cardiac development and pediatric cardiology. These include computer experiments on the flow pattern of the heart at different stages of development, simulation of the changes in the heart occurring at birth, and the development of computer models of congenital heart disease.